title: Good accuracy of the Phase III Oxford Mobile Bearing Unicompartmental Knee Instrumentation.
abstract: OBJECTIVE
  Unicompartmental knee arthroplasty (UKA) needs careful balancing of flexion/extension (F/E) gaps to prevent dislocation of the mobile meniscal bearing. Assessment of gaps is based on the surgeon's subjective insertion force of a feeler gauge with different thicknesses and/or the lift-off of a trial meniscal bearing. However, the accuracy of this method remains unclear. We assessed the accuracy of the technique.
  
  
  METHODS
  A consecutive series of 33 UKAs in 32 patients (mean age 64 years, 24 women) were balanced using the Oxford Phase III (OP III) Instrumentation. The recommended technique for F/E gap assessment was performed using different feeler gauges with 1-mm increments and the meniscal bearing lift-off tests according to surgical technique. A tensiometer was inserted and both gaps were maximally distracted by hand. Measurements in mm were recorded and analyzed with a reading of 90 N for both gaps in 20 and 90 degrees of flexion.
  
  
  RESULTS
  The gaps measured were 12 (11-18) mm in extension and 13 (11-18) mm in 90 degrees of flexion. The difference between the gaps was 0.4 (-0.5 to 1.0) mm (p < 0.001). There were no statistically significant gender differences regarding composite implant thickness, laxity, flexion gap, extension gap, or gap difference.
  
  
  CONCLUSIONS
  OP III instrumentation using feeler gauges and the lift-off test provides accurate balancing of F/E gaps with an accuracy of less than 1 mm.
authors.affiliation: Department of Orthopedics, Trauma Surgery and Paraplegiology, Heidelberg University Hospital, Heidelberg, Germany.
authors.forename: Rudi G
authors.initials: RG
authors.lastname: Bitsch
authors.forename: Arvind von
authors.initials: Av
authors.lastname: Keudell
authors.forename: Elena
authors.initials: E
authors.lastname: Losina
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Fitz
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation* / Q000379:methods; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000601:surgery*; D007720:Knee Prosthesis / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery*; D011446:Prospective Studies; D016059:Range of Motion, Articular; D016896:Treatment Outcome